Spirit level

ABSTRACT

A spirit level comprising a hollow rectangular bar of extruded material formed with at least one recess for receiving a bubble tube and having end caps for closing the ends of said bar; together with a sealed capsule, mountable adjacent said recess, containing a bubble tube and adjustment mechanism therefor.

BACKGROUND OF THE INVENTION

This invention relates to spirit levels and is particularly directed tospirit levels which are uniquely suited to mass production and whichprovide unique protection of the bubble tube against contamination bydirt, grease or the like.

Spirit levels have long been useful in carpentry and construction workfor assuring that a surface is truly horizontal or vertical.Traditionally, spirit levels have comprised one or more slightly arcuatetubes substantially filled with fluid but containing an air bubble. Bymounting these "bubble tubes" on an elongated bar, with the curve lyingconvexly with respect to the surface of the bar, the air bubble willtend to move toward the center or high point of the tube and, bycalibrating the device on a known level surface and providing sightlines at the center or opposite edges of the bubble, the device can beused subsequently to measure the levelness of an unknown surface.Customarily, one or more adjustment screws are provided to permit slightmovement of the bubble tube during calibration. Unfortunately, spiritlevels are frequently used in carpentry or construction areas wherethere is considerable dust, sawdust, grease and the like which canintrude into the region about the bubble tube and can interfere with thepositioning and calibration of the bubble tube. Furthermore, themounting, positioning and calibration of the bubble tube on the bar has,in the past, required a considerable amount of manual labor, which hasrestricted or prevented the mass production of spirit levels and,consequently, has caused them to be relatively expensive.

A search in the U.S. Patent Office has revealed the following patents:

    ______________________________________                                        U. S. Pat. No.                                                                              Inventor    Issued                                              ______________________________________                                          353,846     G. Cook     Dec. 7, 1886                                          421,786     J. A. Traut Feb. 18, 1890                                         465,882     C. E. Peterson                                                                            Dec. 29, 1891                                       1,017,646     G. Broadmore                                                                              Feb. 20, 1912                                       1,515,239     H. J. Cook  Nov. 11, 1924                                       1,815,949     O. Marischal                                                                              July 28, 1931                                       2,101,077     A. Langsner Dec. 7, 1937                                        2,301,769     F. A. Babcock                                                                             Nov. 10, 1942                                       2,557,291     R. T. Hubbard                                                                             June 19, 1951                                       2,567,553     C. P. Davey Sept. 11, 1951                                      4,299,035     S. Stauber  Nov. 10, 1981                                       4,542,592     R. E. Hopkins                                                                             Sept. 24, 1985                                      ______________________________________                                    

The patents to Broadmore and G. Cook each disclose spirit levels whereinthe bubble tube is protected from invasion by dirt, but each requireconsiderable manual labor to assemble and calibrate. The remainingpatents each disclose spirit levels in which the bubble tube and theadjusting mechanism therefor are exposed and susceptible to invasion bydirt and dust. Thus, none of the prior art devices are entirelysatisfactory.

These disadvantages of prior art spirit levels are overcome with thepresent invention and a spirit level is provided which totally precludesintrusion of dirt, dust or the like into the region of the bubble tubeor its adjustment mechanism, yet which requires minimal manual labor forassembly and calibration and, hence, is particularly well suited to massproduction.

The advantages of the present invention are preferably attained byproviding a spirit level formed of a hollow, rectangular bar of extrudedmaterial having end caps for closing the ends thereof and formed withrecesses formed in said bar for receiving bubble tubes; together with asealed capsule, mountable adjacent said recesses, containing a bubbletube and adjustment mechanism therefor. Because the bubble tube andadjustment mechanism are sealed within the capsule, invasion by dirt ordust is virtually precluded. Moreover, should the capsule or itscontents become damaged in any way, they can readily be removed andreplaced. Also, the capsules can be produced independently, in anydesired quantity, and can be assembled quickly and easily with theextruded bar and end caps to permit mass production of spirit levelsembodying the present invention.

Accordingly, it is an object of the present invention to provideimproved spirit levels.

Another object of the present invention is to provide improved spiritlevels which virtually preclude invasion of the region about the bubbletube or its adjusting mechanism.

An additional object of the present invention is to provide spiritlevels which are uniquely adapted to mass production.

A further object of the present invention is to provide spirit levelswherein the bubble tube can be replaced quickly and easily.

A specific object of the present invention is to provide a spirit levelcomprising a hollow rectangular bar of extruded material formed with atleast one recess for receiving a bubble tube and having end caps forclosing the ends of said bar; together with a sealed capsule, mountableadjacent said recess, containing a bubble tube and adjustment mechanismtherefor.

These and other objects and features of the present invention will beapparent from the following detailed description, taken with referenceto the figures of the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a spirit level embodying the presentinvention;

FIG. 2 is an exploded isometric view of the bubble tube capsule of thespirit level of FIG. 1;

FIG. 3 is a transverse section through the assembled bubble tube capsuleof FIG. 2 taken on the line 3--3 of FIG. 2; and

FIG. 4 is a side view of one of the end caps of the spirit level of FIG.1.

DETAILED DESCRIPTION OF THE INVENTION

In that form of the present invention chosen for purposes ofillustration in the drawing, FIG. 1 shows a spirit level, indicatedgenerally at 10, comprising a hollow, rectangular bar 12, of extrudedmaterial, such as metal or a rigid plastic, formed with recesses 14 and16 for receiving bubble tube capsules 18. End caps 20 are provided forclosing the ends of the bar 12. The end caps 20 may be formed ofsubstantially any desired material and, as best seen in FIG. 4, areformed with a rearwardly projecting flange 22 spaced slightly inwardfrom the peripheral edges 24 of the end cap 20 and serving tofrictionally engage the interior of the hollow bar 12 to releaseablyretain the end cap 20 in position to close the end of the bar 12 againstinvasion by dirt, dust or the like.

The bubble tube capsules 18 are identical and, as best seen in FIGS. 2and 3, each comprises a hollow, box-like structure having a top 26 andbottom 28 which overlie a pair of side walls 30 and right and left endpieces, seen at 32 and 34 respectively. The top 26, bottom 28, sidewalls 30 and end pieces 32 and 34 are preferably formed of rigid,transparent material, such as plastic, and are sized to nest together toform the box-like capsule 18, as seen in FIG. 3. Finally, a cylindricalbubble tube 36 is provided containing a suitable fluid and having asmall bubble 38 therein, as is well known in the art. The upper surfacemay be curved for magnification purposes well known in the art.

To assemble the bubble tube capsule 18, a circular recess 42 is formedextending part way through the left end piece 32 which is large enoughto loosely receive the left end of the bubble tube 18 and a layer 44 ofresilient material, such as polyurethane silicone, is provided about theend of the bubble tube 18 to serve as a resilient cushion and adhesive,securing the tube 18 in position within the recess 42.

Similarly, a vertically-elongated oval recess 46 extends part waythrough the right end piece 34 to slideably receive the right end of thebubble tube 18, while allowing room for avertical movement of the bubbletube 18 by the adjustment mechanism. To form the adjustment mechanism, avertical recess 48 is formed within the right end piece 34 andcommunicates with the bottom of the oval recess 46, as best seen in FIG.3. A spring 50 is located within the vertical recess 48 and bearsagainst the bottom of the end of the bubble tube 18 to urge the rightend of the bubble tube 18 upward within the oval recess 46. Finally, athreaded opening 52 extends vertically through the top 26 at a pointspaced from the right end thereof and an Allen screw 54, or the like, isthreaded into the opening 52 to bear against the upper surface of thebubble tube 18, as seen in FIG. 3. Threading the Allen screw 54 inwardlywill serve to force the right end of the bubble tube 18 downward withinthe oval recess 46, while threading the Allen screw 54 outwardly willpermit spring 50 to urge the right end of the bubble tube 18 upwardlywithin the oval recess 46.

To produce the spirit level 10 of FIG. 1, the hollow, rectangular bar 12of extruded material is provided and the recesses 14 and 16 are formedin the bar 12. Then, bubble tube capsules 18 are secured within the bar12 adjacent the recesses 14 and 16 by suitable means, such as adhesive,and end caps 20 are frictionally urged into position to close the endsof the bar 12. The spirit level 10 may be calibrated by placing the bar12 on a known level surface and adjusting the neutral position of thebubble 38 within the bubble tube 36 of the capsule 18 by appropriaterotation of the Allen screws 54. Subsequent recalibration of the spiritlevel 10 may be accomplished, in the same manner, whenever necessary ordesirable. Moreover, should one of the bubble tube capsules 18 becomedamaged in any way, it can quickly and easily be removed and replaced byanother similar bubble tube capsule 18.

If desired, the upper surface of Top 26 and/or alternately the bubbletube 36 may be formed somewhat convex, as seen at 40 and in FIG. 2, toprovide magnification adjacent the neutral position of the bubble 38within the bubble tube 36. Also, if desired, the bottom 28 and sidewalls 30 of the bubble tube capsule 18 may be provided with reflectivetape to facilitate viewing of the bubble 38 within the capsule 18.Moreover, if desired, an opening 56 may be provided through the end cap20 adjacent the recess 16 of the bar 12 to permit access to the Allenscrew 54 of the adjacent one of the bubble tube capsules 18 withoutrequiring removal of that end cap 20.

In addition, numerous other variations and modifications may be madewithout departing from the present invention. Therefore, it should beclearly understood that the form of the present invention describedabove and shown in the accompanying drawings is illustrative only and isnot intended to limit the scope of the present invention.

I claim:
 1. A spirit level comprising:a hollow rectangular bar ofextruded material formed with at least one recess for receiving a bubbletube capsule, a pair of end caps of closing the ends of said bar, asealed bubble tube capsule mountable within said bar adjacent saidrecess and containing a bubble tube and adjustment mechanism therefore,wherein said bubble tube capsule comprises a top, a bottom, two sidewalls and two end pieces composed of rigid, transparent material andforming a box-like structure; a cylindrical tube substantially filedwith liquid and having a bubble therein, said tube being mounted withinsaid box-like structure, adjusting mechanism located within saidbox-like structure for adjusting the position of said tube, wherein saidbubble tube capsule further comprises: a circular recess extending partway through one of said end pieces formed to slideably receive one endof said tube, a quantity of resilient adhesive material flexiblysecuring said one end of said tube within said circular recess, avertically elongated oval recess formed in the other of said end piecesto slideably receive the opposite end of said tube, a threaded openingextending vertically through said top of said capsule at a point fromsaid other of said and pieces, and screw means threaded through saidthreaded opening and engaging the upper surface of said tube andpositionable to drive said opposite end of said tube downwardly againstthe action of said spring.
 2. The spirit level of claim 1 wherein saidadjusting mechanism comprises:a vertical recess formed within said otherof said end pieces and communicating with the bottom of said ovalrecess, a spring located within said vertical recess and bearing servingto urge said opposite end of said tube upward, a threaded openingextending vertically through said top of said capsule at a point spacedfrom said other of said end pieces, and screw means threaded throughsaid threaded opening and engaging the upper surface of said tube andpositionable to drive said opposite end of said tube downwardly againstthe action of said spring.
 3. A bubble tube capsule comprising:a top, abottom, two side walls and two end pieces composed of rigid, transparentmaterial and forming a box-like structure: a cylindrical, or tubesubstantially filled with liquid and having a bubble therein, said tubebeing mounted within said box-like structure, adjusting mechanismlocated within said box-like structure for adjusting the position ofsaid tube, wherein said bubble tube capsule further comprising: acircular recess extending part way through one of said end pieces formedto slideably receive one end of said tube, a quantity of resilientadhesive material flexibly securing said one end of said tube withinsaid circular recess, a vertically elongated oval recess formed in theother of said end pieces to slideably receive the opposite end of saidtube, and magnification means on one of said top wall and cylindricaltube for ease of reading said bubble in said cylindrical tube.
 4. Thebubble tube capsule of claim 3 wherein said adjustment mechanismcomprises:a vertical recess formed within said other of said end piecesand communicating with the bottom of said oval recess, a spring locatedwithin said vertical recess and bearing serving to urge said oppositeend of said tube upward, a threaded opening extending vertically throughsaid top of said capsule at a point spaced from said other of said endpieces, and screw means threaded through said threaded opening andengaging the upper surface of said tube and positionable to drive saidopposite end of said tube downwardly against the action of said spring.5. A spirit level comprising:a hollow rectangular bar of extrudedmaterials formed with at least one recess for receiving a bubble tubecapsule, a pair of end caps for closing the ends of said bar, a sealedbubble tube capsule mountable within said bar adjacent said recess andcontaining a bubble tube and adjustment mechanism therefor, wherein saidbubble tube capsule comprises: a top, a bottom, two side walls and twoend pieces composed of rigid, transparent materials and forming abox-like structure; a cylindrical tube substantially filled with liquidand having a bubble therein, said tube being mounted within saidbox-like structure, and adjusting mechanism located within said box-likestructure for adjusting the position of said tube, wherein said bubbletube capsule further comprises: a circular recess extending part waythrough one of said end pieces formed to slideably receive one end ofsaid tube, a quantity of resilient adhesive material flexibly securingsaid one end of said tube within said circular recess, a verticallyelongated oval recess formed in the other of said end pieces toslideably received the opposite end of said tube.
 6. The spirit level ofclaim 5, wherein said adjusting mechanism comprises:a vertical recessformed within said other of said end pieces and communicating with thebottom of said oval recess, a spring located within said vertical recessand bearing serving to urge said opposite end of said tube upward, athreaded opening extending vertically through said top of said capsuleat a point spaced from said other of said end pieces, and screw meansthreaded through said threaded opening and engaging the upper surface ofsaid tube and positionable to drive said opposite end of said tubedownwardly against the action of said spring.
 7. A bubble tube capsulecomprising:a top, a bottom, two side walls and two end pieces composedof rigid, transparent material and forming a box-like structure; acylindrical tube substantially filled with liquid and having a bubbletherein, said tube being mounted within said box-like structure, andadjusting mechanism located within said box-like structure for adjustingthe position of said tube, and said tube capsule further comprising: acircular recess extending part way through one of said end pieces formedto slideably receive one end of said tube, a quantity of resilientadhesive material flexibly securing said one end of said tube withinsaid circular recess, a vertically elongated oval recess formed in theother of said end pieces to slideably received the opposite end of saidtube, and magnification means on one of said top wall and cylindricaltube for ease of reading said bubble in said cylindrical tube, andwherein said adjustment mechanism comprises: a vertical recess formedwithin said other of said end pieces and communicating with the bottomof said oval recess, a spring located within said vertical recess andbearing serving to urge said opposite end of said tube upward, athreaded opening extending vertically through said top of said capsuleat a point spaced from said other of said end pieces, and screw meansthreaded through said threaded opening and engaging the upper surface ofsaid tube and positionable to drive said opposite end of said tubedownwardly against the action of said spring.